W: The repository 'https://download.kopano.io/supported/mdm:/final/Debian_9.0 Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'https://download.kopano.io/supported/webmeetings:/final/Debian_9.0 Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch https://download.kopano.io/supported/mdm:/final/Debian_9.0/Packages 404 Not Found
E: Failed to fetch https://download.kopano.io/supported/webmeetings:/final/Debian_9.0/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

for me, it seems that needs some update on the repos is required and it’s not my fault. Or is it ?! All other repos are just working (webapp, core, etc)…